Minimizing edge cracking losses



April 1964 E. J. RIPLING 3,129,503

MINIMIZING EDGE CRACKING LOSSES Filed Feb. 26, 1960 FIG-.1

TIELE 5 L. 5' z j 50 52 INVENTOR.

EDWAQD J. Emuua BY 7 62%., fi l dd 2,

ATTORNEYS United States Patent Can Company, Inc, New York, N.Y., a corporation of N ew York Fiied Feb. 26, 195i), Ser. No. 11,213 4 Claims. (Cl. 29-528) This invention relates to the minimizing of scrap losses by reason of cracking during the rolling of metal.

In the rolling of ingots and slabs to form thinner material such as plates, strips and laminate stock, the edges develop irregularities, with cracks extending inward. This requires trimming, often both during the course of the rolling and in determining the final width of the product: thus, continued rolling of a strip having edge cracks can cause these to propagate across the entire width. Since the plate or strip must be free of edge cracks throughout its length, the inward extension of the longest crack determines the scrap which must be trimmed away at the corresponding edge, e.g., before coiling. Such trimming not only represents an economic loss in the scrap, but also the labor and equipment costs in determining the extent of trimming needed and in performing the operation. The extent of edge cracking depends upon the metal: with high strength aluminum alloys such as 2024 or 7075, and a normal heating and rolling schedule, the scrap loss can be 15 percent, while with a softer metal, such as 6061 or 5052, the loss can be 5 to 7 percent. For example, hot rolled slabs of 2024 or 7075 aluminum alloy which are one inch thick may have visible cracks extending inward for two inches. With some aluminum-magnesium binary alloys, the trimming can become so extensive that no commercially rolled products are available.

This trouble is even more serious when a laminate stock is to be rolled as a strip which is to be opened into a tubular form. Here, any penetration of an edge crack to the area occupied by the discontinuity which separates the laminations means that the section of the strip having such an actual or incipient break must be discarded, noting that the actual visible break may not appear until all operations including the opening and testing of the tubing for continuity of surface have been performed.

It is believed that metals crack from their edges during rolling, rather than from an interior position, because the edges are free surfaces and are subjected to a uniaxial compressive stress, whereas the interior of the metal is under triaxial compression during the reduction roller action. Also, as the metal spreads during rolling, a tensile component of force develops at the edge, and contributes to the formation of edge cracking: and this effect is particularly involved when the cast structure is of a hard alloy susceptible to cracking. Comparably, a rod pulled at its ends, i.e., with uniaxial tension, breaks at some point after a moderate amount of deformation: whereas, during extrusion of the same metal, a rod can be successfully deformed to a thin Wire without fracturing, due to the triaxial forces.

The state of the metal at the beginning of a specific rolling step is important. Thus an ingot, when heated for hot rolling, has a cast structure which is generally brittle, and will form edge cracks while the major body or bulk of the metal is confined by the triaxial compression: splitting at the edges, and cross-cracking can develop. Likewise, with hot-short metals, the trouble arises. In general, cracking develops during the early blooming or break-down passes, and may be present as invisible hair cracks so that early trimming does not remove all the damaged stock.

According to the present invention, the troubles of edge cracking are avoided by providing the edges of the original billet of metal which of itself is not subject to the 3,129,503 Patented Apr. 21, 1964 difficulty and which acts to control the cast metal during the break-down rolling and to keep it under triaxial forces, so that cracks do not develop therein.

An object of the invention is the preparation and rolling of ingots of metal subject to edge cracking during the usual rolling, by providing the edges with integrated metal portions which are not so subject.

Another object of the invention is the preparation and rolling of ingots of metal subject to edge cracking during the usual rolling, by providing the edges with integrated portions of metal having already a worked structure.

Another object of the invention is the preparation and rolling of ingots of metal subject to edge cracking, by providing the edges with integrated portions of softer metal.

Another object of the invention is the provision of composite integrated billets having the major and central bulk of cast metal subject to edge cracking during the normal rolling, and lateral portions of metal not so subject, and competent of rolling into strip material without the development of edge cracking in the major metal.

A further object of the invention is the preparation of laminate stock in which the laminations are of metal subject to edge cracking during the usual rolling, by preparing composite billets having integrated major cen-. tral portions of cast metal and lateral portions of a metal essentially free of edge cracking, and rolling the same to produce a laminate strip stock wherewith the lateral portions prevent the development of cracks in laminations.

With these and other objects in view, as will appear in the course of the following description and claims, illustrative embodiments of the inventive practice are shown on the accompanying drawings, in which:

FIGURE 1 is a perspective view of a first composite billet according to this invention;

FIGURE 2 is a perspective view of a part of a strip prepared by rolling the billet of FIGURE 1, indicating the minor edge trimming;

FIGURE 3 is a perspective view of a hollow composite billet;

FIGURE 4 is a perspective view of a part of a strip prepared by rolling the billet of FIGURE 3 with a laminar portion shown in partly opened form;

FIGURE 5 is a conventionalized diagram of apparatus for forming the billets of FIGURES 1 and 3.

In FIGURE 1, a composite billet is shown as having the major central portion 10 of material formed by casting metal between the lateral edge portions 11 of a more ductile metal, so that integrating bonds or Welds 12 are formed as shown by the hatched lines over the interfaces. Such a billet can be then heated and rolled, wherewith during the early break-down or blooming passes, the cast portion 10 and the edge portions 11 extend regularly, with the edge portions preventing rapid cooling at the interfaces and serving to confine the metal of portion 10 so that hair cracks parallel or at right angles to the edges are prevented therein. As the rolling progrmses, the cast structure becomes fibrous and more resistant to cracking, but can undergo work-hardening as the rolling temperature drops. As the end of the rolling, when the strip or plate 15, FIGURE 2, has been reduced to gage, the portions are of the same thickness, with the central portion 10 of hard metal still integrated with the edge portions 11- at the interfaces at the bonds 12. When a different metal, e.g., pure aluminum or a softer aluminum alloy is employed for the edge portions of a billet having the central portion of a harder alloy and sheets or strips of this harder alloy are the desired product, the edge portions 11 can now be trimmed away along the planes of these bonds with essentially no edge loss of the central portion 10 of the strip. When the edge portions are of worked metal of the same analysis as that of the central cast portion, the entire width of the rolled strip can be employed, because edge cracking of the edges has been avoided. Further, when a coil is to be formed of strip having the same billet analysis for the edge portions and cast central portion, the trimming can be done by spaced severing means for determining the width of the strip, regardless of whether the severances are in the residue of the central portion or in the residues of the edge portions, e.g., the presence of longitudinal camber can be disregarded in producing a coil of strip material having parallel rectilinear edges as severed.

The metals for the central portion and the edge portions 11 are selected for their ability to integrate along abutment interfaces without forming a brittle interalloy film, to undergo the schedule of heating and reduction together, and to withstand cleaning operations. There should be mutual solid solubility, but disparity of tensile strength or yield strength is of very minor importance in practice. For example, when aluminum alloys 6061, 2024 or 7075 are to be employed for the central portion 10, the edge portions 11 can be of a softer and more easily rolled material such as 1100 alloy or pure aluminum. It is also feasible to use pre-worked edge portions of the same alloy, that is, metal which has been wrought to break down the cast structure and therewith render it less subject to edge cracking: for example, wrought pieces of 6061 alloy may be employed with the same 6061 alloy cast therebetween and integrated by the bonding; with 2024 cast alloy for the center portion 10, the edge portions 11 can be of wrought 2024 alloy. When the edge portions 11 are of softer metal, e.g., 1100 alloy or commercially pure aluminum, these may be used as cast, or after working, or as extrusions: noting that such alloys inherently are less subject to edge cracking than the harder alloys. During the casting of the harder alloys, e.g., of relatively high copper content, phase separation can occur with low melting and brittle phases forming a semi-continuous brittle network in the structure, so that cracking will occur from the edges and along such network during the usual unprotected rolling. When the metal is hot-short, e.g., 2024 aluminum alloy, the presence of the integrated edge portions prevents the exhibition of such effects at the central cast structure; wherewith the need of initial passes with minor reductions per pass, can be avoided, and the entire rolling conducted with a lesser number of passes, with lesser cooling during the rolling, and consequent cost saving in the time of rolling and expense of reheatings.

The invention is applicable to metals which exhibit edge cracking when homogeneous billets thereof are rolled. Edge portions of commercially pure aluminum, 2-8 or 1100 aluminum alloy can be used with aluminum alloys such as 2024, 5052, 5154, 6061, 7075 or the like. Thus, with a tool steel or a steel alloy, such as rephosphorized MC-T6 steel, edge portions of low carbon steel can be employed. Commercially pure copper can be employed for the edge portions with a central portion of silicon or tin bronzes. It will be noted that, in the stated illustrations, the edge portions are of less expensive material than the cast metal.

The edge pieces constitute about 2 to 4 percent of the width of the ingot: for example, with an ingot which is 36 inches wide, the individual pieces constitute /1 to 1 /2 inches at the respective lateral edges.

It is preferred to have the major alloy component of the central portion present in the metal for the edge portions; both for facility of welding or bonding together without forming a brittle interface zone, and for permitting cleaning operations such as pickling. Likewise, it is preferred to have the edge portions of a metal which is of the same or a higher melting point than the metal to be poured for forming the central portion: and this is feasible when a higher content of the base metal is in the edge portions than in the central portion. For example, pure aluminum and low-copper, etc., aluminum alloys are higher melting than high copper, etc., aluminum alloys: wrought iron and 20 point carbon steels are higher melting than tool steels and alloys steels: copper is higher melting than the stated bronzes. Such melting point relationship is advantageous in assuring the bonding integration during casting, without fusing the bodies of the edge portions.

In the practice shown in FIGURES 3 and 4, the composite billet has a longitudinal channel 19 between the central masses 20 of the cast metal, and the edge portions 21 are integrated with the central masses 20 along the abutment interfaces 22. The metals for the parts 20, 21 can be as set out above for the parts 10, 11. The channel 19 can then be filled with an antiwelding or resist material such as aluminum oxide, zirconia, or other inert fine powder, with sodium chloride or other soluble salt which is solid at the hot rolling temperature, or with an organic compound such as polyethylene, polypropylene, epoxy resin, polyvalent metal stearate, polycarbonate resin, linear polyamide resin, silicone resin, phthalic-polyglycol ester, novolac phenolic resin, polymethyl styrene resin, cyclic terpene polymer resin; and the billet subjected to hot rolling. When an organic compound is employed, the channel ends should be sealed after filling, to protect the compound against air access during the heating and early rolling stages and during the distribution of the resin along the channel with permissive escape of excess under roll pressure.

After the billet of FIGURE 3 has been rolled, the edge portions 21 can be detached as in FlGURE 4, and the laminations 24 resulting from the central masses 20 of originally cast metal can be bent apart to form a tubu lar structure. Therewith, the presence of the edge portions 21 during rolling has protected the central portions 20 against edge cracking or the formation of weaknesses extending along the length adjacent the lateral edges of the channel 19.

The ingots of FIGURES 1 and 3 can be cast in static molds or by the semi-continuous method conventionally shown in FIGURE 5. The mold 50 has an open bottom which is closed by a platform 51 at the beginning of the casting. The pre-formed edge portions 11 or 21. are connected to the platform as by wedges 52 and extend upward against the end surfaces of the mold S0 and are guided, for downward movement, as by rollers 53 mounted above the mold. It is preferred to preheat the edge pieces 11 or 21 before entry into the mold for receiving the cast metal: e.g., they may be heated to near the respective melting point. Further, the bonding can be facilitated by applying a flux to the surfaces which are to be bonded, for example, by nozzles 48 which deliver a fiux such as a metal chloride with aluminum edge pieces onto the inner surfaces, with the inner rollers 53 acting to spread this flux as thin layers upon the pieces as they move downward. Metal is supplied to the tundish 54 and passes downward into the mold through a valved drop tube. The initially poured metal weld-bonds to the edge pieces and solidifies adjacent the platform 51, forming a liquid level near the top of the mold, with a liquidzsolid interface as illustrated by the line 55. The bonding can be facilitated by vibrating the metal at the interface of solid and molten metal, for example, by employing vibrators 49 which impose forces upon the edge portions 11, 21 above the bold 50 so that the inner faces of the edge portions move toward and from the molten metal by a small amount, e.g., a few thousandths of an inch, and an effect similar to cavitation is produced which induces wetting as the portions move downward. Such vibrators may be energized electrically, by an alternating current of 60 cycles per second or higher. The platform is lowered, as by the ram 56; and the entering flow of metal and the downward movement of the platform with the solidified part of the ingot thereon are coordinated so that the ingot forms and progresses downward. When the desired length of ingot has been formed, the flow of metal is stopped, and the metal in the mold allowed to solidify. The lower wedges are removed, and the ingot is separated from the platform and taken out. New edge portions are inserted, and the metal flow started again with the platform raised. When a hallow ingot is to be made, one or more core pieces can be supported in the mold, corre sponding to the number of channels desired, and the pouring done as before. After cooling, if the cores are of bonded refractory powder, the billet can be rolled; if the cores are of non-welding material, e.g., steel with aluminum ingot metal, they can be pulled out, and the channels filled with resist before rolling.

Illustratively, by casting 6061 aluminum alloy between edge pieces of 1100 (2-S) edge pieces, the resultbillet has been rolled to a gage of 0.020 inch and below without edge cracking; whereas an ingot of 6061 alloy alone formed serious edge cracks.

It is obvious that the invention is not limited to the specific illustrative embodiments, but can be employed in other ways within the scope of the appended claims.

What is claimed is:

1. The method of producing a laminate metal strip having surface laminations separated from one another by an internal discontinuity extending parallel to the opposite surfaces of the strip, and having integral metal connections between said laminations at the marginal edge portions of the strip, which comprises providing wrought edge pieces of relatively ductile metal, providing a channel-forming core between the edge pieces, casting a less ductile metal between the edge pieces to become integrally bonded therewith and around the core whereby the core forms an internal channel in the billet extending along the same and in the direction from one edge portion toward the other and with the lateral edges of the channel being laterally spaced from the edge pieces, rolling the composite billet with a material in said channel to prevent welding together of the surface laminations being formed from the cast metal, wherewith the edge pieces provide integrated marginal portions of the metal strip and the cast metal portions therebetween provide said surface laminations nad integrated portions connecting the surface laminations, and removing marginal portions from the rolled strip along longitudinal lines spaced from and between the longitudinal edges of the rolled strip and the respective adjacent longitudinal edge of the rolled residue of said channel.

2. The method of producing a laminate metal strip having surface laminations of a metal which exhibits edge cracking during initial hot rolling from the cast ingot, said laminations being separated from one another by an internal discontinuity extending parallel to the opposite outer rolled surfaces of the strip, said strip having inegral metal connections between said laminations at the marginal edge portions of the strip, which comprises pro viding metal edge pieces which do not exhibit edge cracking during hot rolling and which are capable of welding to the molten metal of said surface laminations, casting the surface lamination metal in two portions between the edge pieces to become integrally bonded thereto while molten and therewith forming a discontinuity between said portions, rolling the composite billet with a material present at said discontinuity for preventing welding together of said portions during rolling and with the edge pieces providing the marginal portions of the metal strip wherewith the edge pieces are effective to confine the said cast metal and prevent edge cracking thereof, and removing marginal portions from the rolled strip along longitudinal lines spaced from and between the longitudinal edges of the rolled strip and the respective adjacent longitudinal edge of the rolled residue of said channel.

3. The method of producing a worked laminate metal structure from a metal which exhibits edge cracking during initial hot rolling from a cast ingot, which comprises working and trimming parts of the metal to provide wrought edge pieces, placing said edge pieces in a casting mold with a core member between and spaced from the edge pieces, casting other parts of the same analysis metal between said wrought edge pieces to become integrally bonded thereto as a composite billet and therewith employing the core member for forming a channel between the surfaces provided by the cast metal, said channel having a lesser width than the distance between the edge pieces and therewith having its lateral edges spaced from both said edge pieces, introducing an anti-welding material into the channel, hot working the composite billet to form a strip with the residues of the edge pieces at the edges of the strip wherewith the pre-wrought condition of the edge pieces acts to prevent cracking adjacent the edges of the section and into the region of the rolled residue of the anti-welding material, and thereafter removing the residues of said edge pieces from the strip.

4. A billet comprising a mass of cast metal having a longitudinal internal channel therein, and integrally bonded therewith at the lateral edges of said mass longitudinally extending pieces of Wrought and more ductile metal than that of said cast mass, said channel being of elongated cross-section with the larger dimension extending in the direction from one lateral edge to the other and terminating short of the edge pieces, the integral bonded junctions of the cast metal and the wrought metal being welds formed by the action of the molten cast metal upon the wrought metal.

References Cited in the file of this patent UNITED STATES PATENTS 642,158 Russell Jan. 30, 1900 1,281,503 Brunell Oct. 15, 1918 1,348,677 Witter Aug. 3, 1920 2,095,837 Sandler Oct. 12, 1937 2,468,206 Keene et a1 Apr. 26, 1949 2,757,444 Chace Aug. 7, 1956 2,898,667 Orehoski Aug. 11, 1959 2,994,951 Eubank et al. Aug. 8, 1961 ,02 55 Maier et al. Apr. 10, 1962 

1. THE METHOD OF PRODUCING A LAMINATE METAL STRIP HAVING SURFACE LAMINATIONS SEPARATED FROM ONE ANOTHER BY AN INTERNAL DISCONTINUITY EXTENDING PARALLEL TO THE OPPOSITE SURFACES OF THE STRIP, AND HAVING INTEGRAL METAL CONNECTIONS BETWEEN SAID LAMINATIONS AT THE MARGINAL EDGE PORTIONS OF THE STRIP, WHICH COMPRISES PROVIDING WROUGHT EDGE PIECES OF RELATIVELY DUCTILE METAL, PROVIDING A CHANNEL-FORMING CORE BETWEEN THE EDGE PIECES, CASTING A LESS DUCTILE METAL BETWEEN THE EDGE PIECES TO BECOME INTEGRALLY BONDED THEREWITH AND AROUND THE CORE WHEREBY THE CORE FORMS AN INTERNAL CHANNEL IN THE BILLET EXTENDING ALONG THE SAME AND IN THE DIRECTION FROM ONE EDGE PORTION TOWARD THE OTHER AND WITH THE LATERAL EDGES OF THE CHANNEL BEING LATERALLY SPACED FROM THE EDGE PIECES, ROLLING THE COMPOSITE BILLET WITH A MATERIAL IN SAID CHANNEL TO PREVENT WELDING TOGETHER OF THE SURFACE LAMINATIONS BEING FORMED FROM THE CAST METAL, WHEREWITH THE EDGE PIECES PROVIDE INTEGRATED MARGINAL PORTIONS OF THE METAL STRIP AND THE CAST METAL PORTIONS THEREBETWEEN PROVIDE SAID SURFACE LAMINATIONS NAD INTEGRATED PORTIONS CONNECTING THE SURFACE LAMINATIONS, AND REMOVING MARGINAL PORTIONS FROM THE ROLLED STRIP ALONG LONGITUDINAL LINES SPACED FROM AND BETWEEN THE LONGITUDINAL EDGES OF THE ROLLED STRIP AND THE RESPECTIVE ADJACENT LONGITUDINAL EDGE OF THE ROLLED RESIDUE OF SAID CHANNEL. 